472 MOLLUSKS : CEPHALOPODS. 



bile from the two ducts of a very large liver. A fleshy 

 funnel before the neck affords a passage to the water 

 which aerates the gills, and also an exit for the excretions. 

 The eye consists of several membranes, and is covered by 

 the skin, which becomes diaphanous in that particular 

 spot. The ear is a slight cavity on each side near the 

 brain, where a membranous sac containing a little stone 

 is suspended. Cephalopods are marine, and are remark- 

 able for a peculiar and intensely black fluid which they 

 secrete, and which, when they apprehend danger, they 

 eject into the water, thus discoloring it, and enabling the 

 animals to conceal themselves. They are quick in their 

 movements, predaceous, and very voracious. 



SUB-SECTION I. 



THE ORDER OF DIBRANCHIATA, OR TWO-GILLED CEPHALOPODS. 



THIS Order comprises cephalopods which have two 

 branchiae, an ink-gland always present, and, with few 

 exceptions, a rudimentary internal shell. Representa- 

 tives are found in all latitudes, and in open ocean as well 

 as near the shores. The skin of the naked cephalopods 

 contains variously colored pigment-cells ; and these ani- 

 mals have the power of effecting such changes in these 

 cells, that the hues of the skin differ from one moment to 

 another. 



The Dibranchiata embrace Argonautidae, Octopodidae, 

 Teuthidae, Belemnitidae, Sepiadae, and Spirulidae. The 

 first two families have eight arms, and fixed eyes ; the 

 remaining ones have eight arms and two elongated ten- 

 tacles with expanded ends, and movable eyes. 



ARGONAUTID/E, OR PAPER- SAILOR FAMILY. - This 

 Family contains cephalopods which have the dorsal arms 

 webbed at the extremity, secreting a symmetrical con- 

 voluted shell, which is thin and translucent. The argo- 



